There is an increasing need for observations by ocean systems. Underwater systems (such as underwater vehicles) observing and collecting data beneath the ocean surface need to communicate or offload this data to surface locations or above-surface sites (e.g., platforms, ships, satellites). The data acquisition rates for an underwater survey platform or an above-surface site can be on the order of 10 megabytes per second. However, current underwater communication systems are generally very slow. These underwater communication systems communicate using either radio waves or acoustic signals. Radio waves have very poor penetration underwater, except at extremely low frequencies, thereby limiting bandwidths and data rates. Acoustic modems have modest data rates at even short ranges. However, at long ranges and lower frequencies the data rates of acoustic modems can drop below 1 kilobit/s.
One technique for offloading data is to allow the underwater device to reach the surface and then communicate with other above-surface sites using radio waves. Another technique is to connect the underwater device to a docking port also located underwater, whereby the docking port is connected to the surface via a tether. Another technique is to recover the underwater device and directly download the collected data.
However, these techniques have limitations. None of them work effectively while the vehicle is underway and underwater. Radio communications can achieve reasonable data rates when line of sight is available and the antenna is not being washed over by waves (a fairly significant problem for small vehicles). Underwater docks don't require the vehicle to surface but require infrastructure that is not typically available in unexplored areas. Recovering the vehicle is slow, cumbersome, and requires a ship in the general proximity of the vehicle. What is needed is a way to remotely get large amounts of data from a vehicle back to a ship or shore.